There is a customer that for the past couple years has been complaining about her pool constantly having a fine grayish dust on the bottom of the pool. It's not present when the cover is removed for the opening ( we do vacuum on prior to closing ). But after she has the pool running the dust comes back (and quickly comes back after she vacuums with a battery operated vacuum . I've collected some of the material and stuck it in a glass of bleach and nothing happened. It stayed the same color and didn't break down. I've racked my mind trying to think of what it can be. I thought it could be outside contamination like pollen (it's an above ground pool with no trees real near by) I thought about maybe the pool ladder having a brick weight that could be breaking down over the years and leaking out. The only thing about that pool that is different from the others I service is the type of chemical she uses. I forget the brand name of the product. But I know it's calcium hypochlorite in a disposable plastic tablet device. Could this be a problem with calcium precipitation? If it is this, do I just tell her to switch to bleach and see if the problem goes away? Or is there another way to test for this or to reduce the precipitation quickly?